"1/3 oct EQ with only one opamp? That sounds interesting, have a page on it?" I have a couple of pro-sound eq made by DuKane that have only one op-amp per channel.They have a single ended class A single transistor input buffer and a single differential gain stage for the filters.The filters are all passive LCR.But a hybrid is also possible.Dynaco used LCR filters for the upper bands and gyrators for the larger low freqency inductors. If you look at the schematic for the McIntosh MQ104 parameric eq it is the same, earlier versions used a single transistor for the gyrator.If you use pots with a center tap and ground the tap the eq is effectively out of circuit with the pot near the center position.My DuKane actually have a switch on each band! These old dinosaurs make the new 60 op-amp stereo models sound really bad.